The invention relates to a plasma picture screen provided with a front plate, which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate provided with a phosphor layer comprising a red and a blue phosphor as well as a green, Tb3+-activated phosphor, with a ribbed structure which subdivides the space between the front plate and the carrier plate into plasma cells which are filled with a gas comprising xenon, and with one or several electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells.
Plasma picture screens render possible color pictures with high resolution and large screen diagonal and have a compact construction. A plasma picture screen comprises a hermetically closed glass cell which is filled with a gas, with electrodes in a grid arrangement. The application of a voltage causes a gas discharge which generates light in the ultraviolet range (145 to 185 nm). This light can be converted into visible light by means of phosphors and be emitted through the front plate of the glass cell to the viewer.
Phosphors which are particularly efficient under vacuum UV excitation are used for plasma picture screens. Frequently used green-emitting phosphors are, for example, Zn2SiO4:Mn (ZSM) and BaAl12O19:Mn (BAL). Both materials show a saturated green emission color with a high y-value of y greater than 0.7. A disadvantage of both materials is their comparatively long decay time t{fraction (1/10)}, for example, 30 ms for Zn2SiO4 with 2.5% Mn. The cause of this is that the transition 4T1xe2x86x926A1 relevant for the emission of the light is spin-forbidden. In addition, the decay time t{fraction (1/10)} and the color point of a Mn2+-activated phosphor are strongly dependent on the Mn2+ concentration. A further disadvantage is the sensitivity of Mn2+ to an oxidation to Mn3+ or Mn4+, which reduces the stability of the phosphors.
By contrast, Tb3+-activated phosphors are temperature stable and photostable, because Tb3+ does not readily oxidize to Tb4+. A further advantage of these phosphors over Mn2+-activated phosphors is their shorter decay time t{fraction (1/10)}, which lies between 2 and 10 ms, depending on the host lattice.
U.S. Pat. No. 6,004,481 accordingly describes a green-emitting Tb3+-activated phosphor for use in plasma picture screens which has the composition (Y1-x-y-zGdxTbyCez)BO3, with 0.0 less than x less than 0.2, 0.01 less than y less than 0.1, and 0.0 less than z less than 0.1.
A major disadvantage of Tb3+-activated phosphors is their yellowy-green color point, which has a low y-value of y less than 0.62.
The invention has for its object to provide a plasma picture screen with a Tb3+-activated phosphor whose green pixels provide light with an improved color point.
This object is achieved by means of a plasma picture screen provided with a front plate, which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate provided with a phosphor layer comprising a red and a blue phosphor as well as a green, Tb3+-activated phosphor, with a ribbed structure which subdivides the space between the front plate and the carrier plate into plasma cells which are filled with a gas comprising xenon, and with one or several electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells, wherein the gas comprises xenon in a proportion of between 5 and 30% by volume.
It is particularly highly preferred that the proportion of xenon in the gas is 10% by volume.
An increased proportional quantity of xenon in the gas surprisingly increases the y-value of the color point of Tb3+-activated phosphors. The result is that the green pixels of a plasma picture screen with a Tb3+-activated phosphor show a sufficiently saturated green.
It is furthermore preferred that the green Tb3+-activated phosphor is chosen from the group (InxGd1-x)BO3:Tb (0xe2x89xa6xxe2x89xa61), Y2SiO5:Tb, CeMgAl11O19:Tb, (Y1-x-yGdxPry)BO3:Tb (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa60.05), GdMgB5O10:Ce,Tb and LaPO4:Ce,Tb.
These Tb3+-activated phosphors are particularly efficient green-emitting phosphors when excited by VUV light.
It may be particularly highly preferable for the green Tb3+-activated phosphor to comprise (Y1-x-yGdxPry)BO3:Tb (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa60.05).
This phosphor has a short decay time t{fraction (1/10)}=8 ms and a high y-value greater than 0.61 of its color point.